Nice catch! I was going from the data shared in that paper[1] and didn't notice that it excluded OpenReview.net (which I'm aware of). The paper got their data[2, 3] from Sciety and it looks like OpenReview isn't included in Sciety's data.
It may have been excluded because OpenReview (as I understand it) seems to be primarily used to provide open review of conference proceedings, which I suspect the article puts in a different category than generally shared preprints.
But it would be worth analyzing OpenReview's uptake separately and thinking about what it's doing differently!
I do agree it's a bit different. How close maybe depends on what motivates you to be interested in the preprint review model in the first place? Could imagine this varies by person.
In a certain sense, the entire field of comp sci has become reorganized around preprint review. The 100% normal workflow now is that you first upload your paper to arXiv, circulate it informally, then whenever you want a formal review, submit to whatever conference or journal you want. The conferences and journals have basically become stamp-of-approval providers rather than really "publishers". If they accept it, you edit the arXiv entry to upload a v2 camera-ready PDF and put the venue's acceptance stamp-of-approval in the comments field.
A few reasons this might not fit the vision of preprint review, all with different solutions:
1. The reviews might not be public.
2. If accepted, it sometimes costs $$ (e.g. NeurIPS has a $800 registration fee, and some OA journals charge APCs).
3. Many of the prestigious review providers mix together two different types of review: review for technical quality and errors, versus review for perceived importance and impact. Some also have quite low acceptance rates (due to either prestige reasons or literal capacity constraints).
TMLR [1] might be the closest to addressing all three points, and has some similarity to eLife, except that unlike eLife it doesn't charge authors. It's essentially an overlay journal on openreview.net preprints (covers #1), is platinum OA (covers #2), and explicitly excludes "subjective significance" as a review criterion (covers #3).
